Method for improving fuel combustion in a furnace and for reducing pollutant emissions therefrom

ABSTRACT

A method for improving fuel combustion in furnaces and the like and for reducing pollutant emissions therefrom, wherein primary air is used solely for fuel feed while commercially pure oxygen without any additives or other constituents is introduced for the combustion of the fuel in regulated amounts so as to provide sufficient oxygen for substantially complete combustion. The oxygen is preferably obtained by separating same from air so that the remaining nitrogen may be used as in inert gas applications.

United States Patent King [ 51 Oct. 24, 1972 [54] METHOD FOR IMPROVINGFUEL COMBUSTION IN A FURNACE AND FOR REDUCING POLLUTANT EMISSIONSTHEREFROM Oliver F. King, 5422 Brae Burn Dn've, Bellaire, Tex. 77401Filed: Feb. 25, 1971 Appl. N0.: 118,836

Inventor:

US. Cl. ..110/1 J, 110/28 R Int. Cl ..F23b 7/00 Field of Search ..1 10/1H, l J, 28 R, 40; 122/479 A References Cited UNITED STATES PATENTSl/l94l De Baufre 122/479 3,048, i 31 Hardgrove ..1 10/28 2,820,438l/1958 Andrews et al 122/479 2,980,082 4/1961 Firl ..122/479 PrimaryExaminer--Kenneth W. Sprague Attorney-Pravel, Wilson & Matthews [57]ABSTRACT 10 Claims, 1 Drawing Figure PATENTEDUBI24 I972 3,699,903

INVENTOR METHOD FOR IMPROVING FUEL COMBUSTION IN A FURNACE AND FORREDUCING POLLUTANT EMISSIONS THEREFROM BACKGROUND OF THE INVENTION turesare higher, improved performance of the super- I BRIEF DESCRIPTION OFTHE DRAWING The FIGURE of the drawings illustrates schematio cally aconventional boiler or steam generator having a produced and dischargedto the atmosphere during combustion when air is used for supporting thecombustion.

In US. Pat. No. 1,720,757, it was proposed that an oxidizing materialsuch as copper oxide be used for supplying free oxygen to maintaincomplete combustion of the fuel in a secondary chamber. However, suchprocedure produced a residue of copper and also introduced additionalcomponents into the stack gases contributing to the pollution upondischarge through the stack.

In US. Pat. No. 2,980,082, it was proposed that the nitrogen in air bereplaced with recirculated combustion gases, on the premise that oxygenalone, or air greatly enriched with oxygen, produced undesirably highfurnace temperatures. However, by recirculating the high temperaturecombustion gases, the tempera tures are actually increased upon eachrecirculation, thus tending to defeat the purpose of using suchcombustion gases. Further, unnecessarily high volumes of inert inactivegases had to be handled, which meant that boiler or furnace sizes had tobe accordingly larger than necessary if designed for just combustionpurposes. Additionally, with such high volume flow, the pure oxygen wasswept out of the stack with the gases that discharged therefrom,reducing the thermal efficiency, and so as to further accentuate the gasvolume and flow velocity required.

SUMMARY OF THE INVENTION The present invention relates to a methodwherein commercially pure oxygen is used alone, preferably instoichiometric quantities, as the secondary or combustion gas, and withonly enough primary air for fuel feed, adequate gas velocities, and fuelturbulence and distribution in the furnace firebox. The commercially,pure oxygen is preferably obtained by separating the oxygen from air sothat the remaining nitrogen can be used for various applications wherean inert gas is desirable. Thus, a twofold purpose is accomplished byremoving the nitrogen from the oxygen in the air. The fuel, such asnatural gas, oil, or coal is introduced into the furnace firebox in acompact, preferably circular configuration, and with the center orvortex thereof as the target area for the substantially pure oxygenstream used for combustion. The combustion zone is thus maintained asdense and compact as possible so that it does not impinge on the furnacewalls or tubes. Because of the higher combustion temperatures, and morecomplete combustion, the flue or stack temperafurnace firebox in whichfuel is burned for the generation of steam. I

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings, the letter Adesignates generally a steam generator or boiler of conventional designhaving a furnace firebox or combustion chamber F in which the fuel isburned. Typically, the boiler or steam generator A has a furnace wall 10which has a plurality of interconnected boiler tubes 12 extendingvertically and disposed in a generally circular or peripheralarrangement on the inside of the wall 10 so as to leave the centralcombustion chamber or firebox F open for the flame of combustion, aswill be more evident hereinafter. The tubes 12 are connected to a steamand water drum 14 in the conventional manner and also to a superheatersection 16, which is also conventional. The superheated steam isavailable and is discharged at line 18 through any suitable controlvalve 19 in such line from the superheater 16. A mud drum 20 isconnected with the steam and water drum 14 and also with the bottom ofthe furnace for collecting solids in the known manner.

The drawing also illustrates a gas flow duct 25 having a conventionaleconomizer section or unit 30 therein for further utilizing the heat inthe exhaust gases. The duct 25 connects with a conventional verticallyextending exhaust stack 35 which is open at the upper end for theexhausting of the exhaust gases to the atmosphere. The height of thestack 35 of course varies in accordance with the location and conditionof draft desired, and it will be understood that the illustration in thedrawings is merely illustrative and is not intended to be limiting as tosize.

In the method of the present invention, the fuel which is introducedinto the firebox or combustion chamber F may be any one of a number ofcommon fuels such as natural gas which is principally methane, orpulverized coal. Also, the fuel may be a liquid such as oil of thebunker C-grade. The fuel is introduced into the combustion chamber orfirebox F by means of one or more fuel burner heads 50 of conventionalconstruction. If the fuel is lump coal, it would be stoker fed as iswell known. The particular construction for each of such fuel burnerheads is dependent upon the particular kind of fuel, i.e., whether it isgaseous, liquid or a solid in the form of small particles.

With the present invention, each of such heads has a port or port meansfor introducing primary air as indicated at 51 with the fuel. In thetypical installation, each fuel burner head has air aspirating ports soas to draw the air in with the fuel as the fuel is injected into thefirebox or combustion chamber F.

The quantity of the primary air which is introduced is specificallylimited in the method of this invention so that it serves mainly toproperly feed the fuel into a compact dense pattern in substantially thecentral portion of the fire chamber F between the burner heads 50 sothat the fuel is in a position for burning away from the furnace walland the tubes 12. Such primary air also serves to control thetheoretical flame temperature, and to provide fuel turbulence anddistribution within the compact but substantially circular pattern ofthe fuel. Also, the volume of the air which is introduced may beregulated to obtain adequate firebox, boiler flue and exhaust stackvelocities and volumes.

Oxygen is introduced in substantially pure form at an oxygen inlet head61 which is connected to a line 62 leading to a source of oxygen whichis substantially pure. Oxygen is sold in commercially pure form, whichmeans that the oxygen has a purity of about 99.99 percent. However,commercial oxygen in tonnage quantities may have a purity as low as 80percent. For the purposes of this invention, the oxygen should besubstantially pure, which means it is within the range of from about 80percent to 100 percent pure.

in the preferred form of the invention, the substantially pure oxygen isobtained by separating the oxygen from the nitrogen in air so that thenitrogen is also available for use as an inert gas in variousapplications such as a nitrogen blanket for disposition over materialsor substances which might have a tendency to burn or explode in an airor oxygen atmosphere. Other uses for the nitrogen will readily occur tothose skilled in the art. It will be appreciated that the separation ofthe nitrogen accomplishes a two-fold purpose since it removes thenitrogen from the air which would otherwise be a pollutant in thecombustion within the furnace and it also makes the nitrogen availablefor use at a point remote from the furnace. The particular manner ofseparating the oxygen and the nitrogen from each other is of course wellknown.

The oxygen is introduced from the head or nozzle 61 so that it feedsinto the center or vortex of the fuel pattern formed by the introductionof the fuel through the burner heads 50. Such control over theintroduction of the oxygen into the fuel tends to confine the flamewithin the central portion of the firebox F so that it does not createhot spots on the furnace wall 10 or the tubes 12. Thus, even though thetheoretical flame temperature is higher than when air alone is used forcombustion, the higher temperatures are controlled-so that they are notdamaging to the furnace itself. In fact, the higher temperatures producemany advantages. For example, with the higher combustion temperaturesand more complete combustion, the flue or stack temperatures are higherand the performance of the superheater and preheater sections of thefurnace or generator A are improved. The actual size of the furnaces maybe reduced as a result of smaller volumes of gas which are moved throughthe furnace with the present invention, and this can result in reducedstack heights and ultimately in improved thermal efficiency. When theexisting furnaces are used with the method of this invention, a smallerflame pattern is created by regulating the burner heads 50. The smallerflame pattern is desirable so that the furnace wall 10 and the surround-6 ing tubes 12 are not subjected to the extremely hot combustiontemperatures in the flame.

As pointed out above, the method of this invention involves a control ofthe quantity of the substantially pure oxygen and the quantity of theprimary air which are introduced intothe firebox so that the oxygennormally constitutes the principal gas for the combustion of the fuel,and the primary air serves essentially only for controlling the flametemperature, for feeding the I fuel into the firebox in the desiredpattern, for discharging the exhaust gases at adequate stack velocitiesand volumes, andfor creating fuel turbulence and distribution.

By way of specific example, when the fuel is methane, a theoreticalflame temperature of about 5 ,500 F. is obtained when the substantiallypure oxygen supplies slightly above 50 percent of the oxygen and theprimary air supplies slightly less than 50 percent of the oxygen instoichiometric relationship to the quantity of the methane. When thesubstantially pure oxygen supplies at least 25 percent of the oxygen andthe primary air supplies the rest, the theoretical flame temperature isabout 4,400 E, as compared to only about 3,700 F. with all primary air.If flame temperatures above 5,500 F. can be tolerated in a furnace, theamount of oxygen supplied in pure oxygen form is increased to supply asmuch as percent of the oxygen while the primary air supplies only 25percent thereof. Under such conditions, the theoretical flametemperature is about 6,500" F. Thus, the advantages of the highertemperatures, plus less pollutants from nitrogen and the otherenumerated advantages over the prior practices are illustrated by suchexamples.

When the fuel is carbon, the theoretical flame temperatures are somewhathigher than when the fuel is methane and the pure oxygen to primary airis the same. For example, when the pure oxygen supplies about 50 percentof the oxygen and the primary air supplies the other 50 percent of theoxygen, the theoretical flame temperature is about 5,680 F. When thepure oxygen supplies about 25 percent of the oxygen, the theoreticalflame temperature is about 4,400 F., whereas such temperature is onlyabout 3,800 F. with all primary air. When the pure oxygen supplies about75 percent of the oxygen and the primary air supplies the other 25percent, the theoretical flame temperature is about 7,500 F. which ishigher than can be tolerated in many furnaces.

It will be understood that the ratio of pure or substantially pureoxygen to the primary air will vary depending upon the fuel used, andthe temperatures which the particular furnace can stand without damage,and therefore, the foregoing examples are not intended to be limiting.

The foregoing disclosure and description of theinvention areillustrative and explanatory thereof, and various changes in the size,shape, and materials as well as in the details of the illustratedconstruction may be made without departing from the spirit of theinvention.

I claim:

1. A method for improved fuel combustion in a furnace firebox or thelike, comprising the steps of:

injecting fuel into a furnace firebox with primary air to an area offuel combustion in the furnace firebox;

feeding substantially pure oxygen in gaseous form into the furnacefirebox separately from said primary air and at the area of the fuelcombustion; and

controlling the quantity of said oxygen and the quantity of said primaryair introduced into the firebox so that said oxygen supplies at leastabout 25 percent of the oxygen for the combustion of the fuel and saidprimary air serves to control the flame temperature, feed the fuel intosaid firebox in said pattern, discharge the exhaust gases at adequatestack velocities and volumes, and create fuel turbulence anddistribution.

2. The method set forth in claim 1, wherein:

the quantity of said substantially pure oxygen and primary air issubstantially equal to the stoichiometric amount necessary for completecombustion of said fuel.

3. The method set forth in claim 1, wherein:

the oxygen provided by said quantity of primary air is less than thequantity of oxygen provided by said substantially pure oxygen.

4. The method set forth in claim 1, wherein said fuel is either gaseous,liquid, or a solid in lump or panicle form when injected into saidfirebox.

5. The method set forth in claim 1, wherein said fuel is natural gas.

6. The method set forth in claim 1, wherein said fuel is pulverizedcoal.

7. The method set forth in claim 1, including:

directing said fuel into the furnace away from the furnace walls ortubes so that localized hot spots do not develop at the elevatedcombustion temperature by direct contact of any part of the furnace withthe flame.

8. The method set forth in claim 1, including:

separating nitrogen from air to obtain said substantially pure oxygenprior to feeding said oxygen into said fuel in said fumace.

9. The method set forth in claim 8, including:

distributing the nitrogen at a point remote from the furnace to form aninert nitrogen blanket.

10. The method set forth in claim 1, wherein:

said substantially pure oxygen is in the range of about 80-100 percentoxygen.

1. A method for improved fuel combustion in a furnace firebox or thelike, comprising the steps of: injecting fuel into a furnace fireboxwith primary air to an area of fuel combustion in the furnace firebox;feeding substantially pure oxygen in gaseous form into the furnacefirebox separately from said primary air and at the area of the fuelcombustion; and controlling the quantity of said oxygen and the quantityof said primary air introduced into the firebox so that said oxygensupplies at least about 25 percent of the oxygen for the combustion ofthe fuel and said primary air serves to control the flame temperature,feed the fuel into said firebox in said pattern, discharge the exhaustgases at adequate stack velocities and volumes, and create fuelturbulence and distribution.
 2. The method set forth in claim 1,wherein: the quantity of said substantially pure oxygen and primary airis substantially equal to the stoichiometric amount necessary forcomplete combustion of said fuel.
 3. The method set forth in claim 1,wherein: the oxygen provided by said quantity of primary air is lessthan the quantity of oxygen provided by said substantially pure oxygen.4. The method set forth in claim 1, wherein said fuel is either gaseous,liquid, or a solid in lump or particle form when injected into saidfirebox.
 5. The method set forth in claim 1, wherein said fuel isnatural gas.
 6. The method set forth in claim 1, wherein said fuel ispulverized coal.
 7. The method set forth in claim 1, including:directing said fuel into the furnace away from the furnace walls ortubes so that localized hot spots do not develop at the elevatedcombustion temperature by direct contact of any part of the furnace withthe flame.
 8. The method set forth in claim 1, including: separatingnitrogen from air to obtain said substantially pure oxygen prior tofeeding said oxygen into said fuel in said furnace.
 9. The method setforth in claim 8, including: distributing the nitrogen at a point remotefrom the furnace to form an inert nitrogen blanket.
 10. THe method setforth in claim 1, wherein: said substantially pure oxygen is in therange of about 80-100 percent oxygen.